The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday.

NSW firefighters baffled by eternal flame

A mysterious fire which has been burning for months under a dry lake in far-western NSW is seemingly thwarting attempts to put it out.

Drivers have reported seeing smoke along a lakebed outside Wilcannia and firefighters, who put the fire out on an almost-weekly basis, are fed up with the eternal flame.

"We thought we had it out about a month ago and just in the last couple of days with some wind, it's popped back up," incident controller Chris Favelle told AAP.

Mr Favelle says he suspects organic material is fuelling the fire.

"There's a little bit of water way out in the middle but it's basically dry, and along the edge, which would have once been the shore 1000 years ago, there's a build-up of organic matter, like sticks and leaves, a bit like peat."

The peat-like matter can burn for a long time but what's baffling the Rural Fire Service is the way the fire dodges all attempts at snuffing it out.

"They get called once a day to put this fire out and they get there and there's nothing," he said.